This invention relates in general to stamping or nibbling machines and in particular to a new and useful stamping or nibbling machine which includes a hollow punch which is driven by a drive member to stamp or nibble a workpiece. The machine includes a spring in its interior located between the inner end of a centering pin and the interior of the punch and provides a displacing mechanism for the centering pin which moves through an opening of a counter die positioned on the other side of the workpiece.
A machine, similar to the invention is disclosed in German AS No. 11 28 259 dated Apr. 19, 1962, for example. By firmly retaining the free end portion of the pin in the directions transverse to the longitudinal axis thereof, pin takes up both the cutting pressure and the shocks caused by the displacement of the tool and workpiece relative to each other. The shocks occur in rapid succession especially in nibbling operations. In the retracted position, the working space between the punch and die is free, so that the workpiece can be inserted and moved without obstacles. Prepunching of the workpiece is not necessary in this prior art machine, this operation is rather effected by the pin in cooperation with an auxiliary die which can be moved in. A powerful drive of the pin is required for this purpose. How this drive is designed cannot be learned from the disclosure. However, it follows clearly from the description that a quite ample space is needed for the drive which moves the auxiliary die and that a special construction is needed for the die which normally operator with the nibbling punch. Consequently, this design does not comply with the needs of an automatic tool change operation, neither on the punch side nor on the die side. This further follows from the fact that because of its separate drive, the pin must project upwardly beyond the tubular punch and that, for changing the tool, both the pin and the punch must be uncoupled. In another embodiment of this prior art machine, the free end of the pin is designed as a drill bit, which makes the auxiliary die dispensable, yet requires a locking device instead, which must be pneumatically or hydraulically actuated in a similar way. In addition, a special drive is needed for the drill, which drive is particularly expensive since the upper end of the drill extends in the direction of the punch drive, which is mostly a crank drive, and the construction in the drive area becomes complicated.